Mistake on a PML Ariel...potential ramifications?

So I've been working on a PML Ariel for the last couple of nights and everything was going well until now. I just finished fitting the motor mount into the body tube. I read the instructions and understood that the piston strap should be fitted between two fin slots, and not in line with one. I read it. I understood it. I vowed to faithfully execute it.

Then I got to carefully applying epoxy 13" up from the end of the body tube for the upper centering ring, carefully making sure the motor mount extended 3/8" beyond the end of the body tube to accommodate the motor retainer, and along the way somehow forgot about making sure the piston strap lined up between two fins. Now that the epoxy has set I see the piston strap is by dumb luck within about 5-10 degrees of one of the fin slots.

My first instinct was to curse my mistake, smash the rocket, throw it in the trash and start over with another kit, but this thing was kind of expensive. Then I got to thinking...*why* is the piston strap supposed to line up *between* two fins and not in line with one?

My best guess is that the strain along the piston strap mount traveling down the motor mount to the fin could snap something loose?

Anyway is this a big deal or not? I noticed the instructions say to make sure the strap is between the fin mounts TWICE and in BOLD LETTERING. That makes it sound PRETTY DAMN IMPORTANT. So should I scrap this thing and start over or is it not that big of a deal?

I'm not 100%, but I think they're just trying to tell you not to let the strap interfere with the fin roots.

As long as the fins still go all the way to the MMT, it doesn't matter at all.

*whew* if that's all it is then I'm good. I suppose I should feel lucky that I didn't by dumb luck get the strap lined up *exactly* with a fin slot.

After looking again I see the upper centering ring is 13" from the bottom of the body tube, the strap is mounted 4" down from there (9" from the bottom of the body tube) but the fin slot starts just under 5.5" from the bottom of the body tube. Even if the piston strap is in line with a fin slot, it should have at least 3" of clearance. That seems like a gigantic margin of error if the only concern is interference between the strap and fin fit. Maybe this instruction applies to other kits with longer fin roots? Or there's something else at work.

muddymooose said:

Maybe this instruction applies to other kits with longer fin roots?

Click to expand...

Could well be the case, the PML instructions are often pretty generic.

As long as the strap does not interfere with the fin roots bonding to the mmt then the rocket will perform just fine.

muddymooose said:

After looking again I see the upper centering ring is 13" from the bottom of the body tube, the strap is mounted 4" down from there (9" from the bottom of the body tube) but the fin slot starts just under 5.5" from the bottom of the body tube. Even if the piston strap is in line with a fin slot, it should have at least 3" of clearance. That seems like a gigantic margin of error if the only concern is interference between the strap and fin fit. Maybe this instruction applies to other kits with longer fin roots? Or there's something else at work.

Click to expand...

Yes, this mattered a great deal on my Explorer. The strap mounting area and fin tabs overlapped by a few inches vertically. If I had not positioned it in between the fin locations, they would not have installed all the way.

I made that gaffe once and had to notch the fin to compensate.

:bang: